Bartonella henselae is an intra-erythrocytic gram-negative bacterium and a causative agent for cat scratch disease in human. An estimated 28% of domestic cats are chronically infected with Bartonella henselae. Infected cats transmit the Bartonella bacteria to people from cat scratches or bites. The disease typically manifests as a regional lymphadenopathy, with some patients presenting with cutaneous lesions at the scratch sites. While cat scratch disease in most healthy individuals is self-limiting, approximately 10% of the patients may develop bacillary angiomatosis, bacillary peliosis, recurrent bacteriemia, and infective endocarditis. (See, e.g., Rochalimaea N., et al., New England Journal of Medicine, 1994, 330: pp. 1509-1515).
Young children and individuals with weakened immune systems are vulnerable to the Bartonella infection. In HIV-1 patients, Bartonella henselae can cause bacillary angiomatosis or peliosis hepatis which may include visceral involvement (Fournier, P. E., and D. Raoult. 1998. Cat scratch disease and an overview of other Bartonella henselae related infections, p. 32-62).
Several diagnostic assays for Bartonella infection are presently available. These include: (i) culturing, (ii) immunofluorescence assay (“IFA”), and (iii) polymerase chain reaction (“PCR”) technologies. Culturing of Bartonella bacteria from blood samples is proven to be tedious and requires an extensive period (i.e., weeks), thus making this assay sub-optimal. Because of varying experimental culture conditions, it adversely affects the reproducibility of the methodology. IFA is not a quantitative assay, and does not provide useful information relating to sensitivity and specificity. In addition, IFAs for Bartonella bacterium have technical issues with cross-reactivity with other human pathogens (e.g., Coxiella burnetii, Rickettsia rickettsii, Ehrlichia chaffeensis, and Treponema pallidum) (Cooper, M. D., M. R. Hollingdale, J. W. Vinson, and J. Costa. 1976. A passive hemagglutination test for diagnosis of trench fever due to Rochalimaea quintana. J. Infect. Dis. 134:605-9). Moreover, IFAs are prone to subjective interpretations by individual technicians. Finally, IFAs are time-consuming and require expensive equipment such as fluorescent microscopes.
PCR technology utilizes the 16S rRNA gene in Bartonella bacterium to detect the presence of the pathogen. PCR has the advantage of simultaneous detection of DNA from multiple Bartonella species (e.g., Bartonella henselae, Bartonella quintana, Bartonella bacilliformis, Bartonella elizabethae, and Bartonella clarridgeiae). The problem with PCR is that it requires the presence of either the organism or its DNA in the test samples at the time of the assay in order to allow species-specific identification. Because of this limitation, PCR assay is only useful during the early stage of infection.
Detection of antigens represents an alternative method of detecting Bartonella henselae. For example, ELISA represents a quantitative detection assay that can provide good sensitivity and specificity. Unfortunately, there are only a limited number of antigens from Bartonella bacterium that have been shown to be useful for serological detection of Bartonella. Loa et al. reported the use of 17-kDa protein from Bartonella in the development of an ELISA (Loa et al., 2007). There is a continuing need for identification of novel Bartonella bacterium antigens useful in serological detection. The present inventors have addressed this deficiency of the prior art and have successfully cloned a gene from Bartonella henselae and expressed the corresponding polypeptide. The present inventors discovered that a 15-kDa polypeptide that is extremely useful in providing an immunoassay to detect the presence of antibodies to Bartonella henselae in patient's sera. The present disclosed antigen is novel and provides an improved clinical diagnostic tool in the field of Bartonella infection.